Vehicle having a nitrogen oxides storage converter and on-board method for monitoring and diagnosing the nitrogen oxides storage converter

ABSTRACT

A vehicle includes a NOx storage converter to receive exhaust gases from a diesel engine, store at least a minimum amount of the NOx at a temperature below a storage threshold, release the NOx at a temperature above a releasing threshold, oxidize hydrocarbon, and oxidize carbon monoxide. An input temperature sensor at an entrance to the NOx storage converter determines an input temperature of the exhaust gases. An output temperature sensor is at an output of the NOx storage converter to determine an output temperature of the exhaust gases. A control module receives the input temperature and the output temperature, determines a magnitude of an exotherm in the NOx storage converter, and stores an electronic fault code in a computer memory in response to the magnitude of the exotherm being below a minimum temperature. The fault code indicates a reduction in a NOx storage capacity of the NOx storage converter.

INTRODUCTION

Some existing vehicles have exhaust gas aftertreatment systems to reducethe amounts of carbon monoxide, unburned hydrocarbons, and nitrogenoxides (collectively, NOx) that are discharged to the atmosphere in theexhaust from internal combustion engines that power the vehicles.Existing exhaust gas aftertreatment systems may be most effective intreating the exhaust from a warmed-up engine because the catalystmaterials have been heated to temperatures (e.g., 200° C. and above) atwhich the catalyst materials serve to effectively oxidize carbonmonoxide and incompletely burned fuel constituents to carbon dioxide andwater, and to reduce nitrogen oxides to nitrogen gas. The existingexhaust gas aftertreatment systems have been effective for both gasolineengines operating at or around the stoichiometric air-to-fuel ratio anddiesel engines (and other lean-burn engines) operating with excess air(sometimes called “lean burn” engines).

It has been difficult to treat exhaust emissions immediately following acold engine start, before the exhaust has heated the catalytic converteror converters to the effective temperatures for designated catalyticreactions. Lean-burn engines, such as diesel engines, tend to producecooler exhaust streams because of the excess air used in the combustionmixtures charged to the cylinders of the diesel engine. Untreated coldstart emissions may make-up a significant portion of the total regulatedemissions at a tailpipe of a vehicle. Mixed nitrogen oxides in theexhaust of diesel engines have been difficult to reduce. These nitrogenoxides include nitric oxide (NO) and nitrogen dioxide (NO₂); the mixturemay be typically referred to as NOx.

SUMMARY

A vehicle includes a NOx storage converter to receive exhaust gases froma diesel engine, store at least a minimum amount of the NOx at atemperature below a storage threshold, release the NOx at a temperatureabove a releasing threshold, oxidize hydrocarbon, and oxidize carbonmonoxide. An input temperature sensor at an entrance to the NOx storageconverter determines an input temperature of the exhaust gases. Anoutput temperature sensor is at an output of the NOx storage converterto determine an output temperature of the exhaust gases. A controlmodule receives the input temperature and the output temperature,determines a magnitude of an exotherm in the NOx storage converter, andstores an electronic fault code in a computer memory in response to themagnitude of the exotherm being below a minimum temperature. The faultcode indicates a reduction in a NOx storage capacity of the NOx storageconverter.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent byreference to the following detailed description and drawings, in whichlike reference characters correspond to similar, though perhaps notidentical, components. For the sake of brevity, reference characters orfeatures having a previously described function may or may not bedescribed in connection with other drawings in which they appear.

FIG. 1 is a block diagram depicting an example of a vehicle with a NOxstorage converter according to the present disclosure;

FIG. 2A and FIG. 2B together show a flow chart that depicts an exampleof a method for monitoring and diagnosing a NOx storage converter on avehicle according to the present disclosure;

FIG. 3 is a graph of experimental results depicting a reduction in theexothermic activity due to oxidation of stored HC in sample NOx storageconverters at different stages of the useful life of the NOx storageconverters; and

FIG. 4 is a bar graph depicting experimental results for the samesamples shown in FIG. 3, except FIG. 4 depicts the NOx storageefficiency for the NOx storage converters below 200° C.

DETAILED DESCRIPTION

Selective Catalytic Reduction (SCR) of NOx using ammonia (NH₃) as areductant is used to reduce NOx emissions from diesel engines that powerexisting vehicles and stationary machines. In the existing SCR process,NOx reacts with a reductant, such as pure anhydrous ammonia, aqueousammonia, and/or ammonia generated by urea decomposition. The reductant(e.g., urea) is injected into the exhaust gas stream before a mixer(e.g., a urea mixer) placed upstream of an SCR catalytic converter. Theexisting ammonia SCR technologies are considered an effective way toreduce diesel NOx emissions when the exhaust system is warmed up and theSCR catalyst has reached an SCR operating temperature.

FIG. 1 is a block diagram schematically depicting an example of avehicle 2 according to the present disclosure. The vehicle 2 is shownhaving an exhaust gas treatment system 10, for the reduction ofregulated exhaust gas constituents (e.g., NOx concentration) from thediesel engine 12. The exhaust gas treatment system 10 described hereincan be implemented in various engine systems that may include, but arenot limited to, diesel engine systems, gasoline direct injectionsystems, and homogeneous charge compression ignition engine systems.

In examples of the vehicle 2 as depicted in FIG. 1, the vehicle 2includes a diesel engine 12 selectively connected to a drivetrain 4 by aclutch 5. The diesel engine 12 is operatively disposed within thevehicle 2. The diesel engine 12 generates exhaust gases as products ofcombustion.

The exhaust gas treatment system 10 includes one or more exhaust gasconduits 14, and one or more exhaust treatment devices. In the exampleillustrated in FIG. 1, the exhaust gas treatment devices include a NOxstorage converter 18, and an SCR converter 22 or a Selective CatalyticReduction in Filter (SCRF) converter 22′. It is to be understood thatthe NOx storage converter 18, the SCR converter 22, and/or the SCRFconverter 22′ may be referred to as catalytic exhaust system components.As can be appreciated, the exhaust gas treatment system 10 of thepresent disclosure may include various combinations of one or more ofthe exhaust treatment devices shown in FIG. 1, and/or other exhausttreatment devices (not shown), and is not limited to the presentexample. For example, a Diesel Exhaust Fluid (DEF) injector 46 may beincluded to inject DEF, i.e. urea, for reducing NOx to nitrogen andwater using NH₃ in the SCR converter 22, or the SCRF converter 22′.

In FIG. 1, the exhaust gas conduit 14, which may include severalsegments, transports exhaust gases 15 from the diesel engine 12 to thevarious exhaust treatment devices of the exhaust gas treatment system10. The NOx storage converter 18 is located downstream of the dieselengine 12 and may include, for example, a flow-through metallic orceramic monolith substrate that may be packaged in a stainless steelshell or canister having an inlet and an outlet in fluid communicationwith the exhaust gas conduit 14. The substrate can have an oxidationcatalyst compound disposed thereon. The oxidation catalyst compound,applied as a washcoat, may contain platinum group metals (PGM) such asplatinum (Pt), palladium (Pd), rhodium (Rh) or other suitable oxidizingand stabilizing catalyst components, or combinations thereof. Theoxidation catalyst is useful in treating unburned gaseous andnon-volatile HC and CO, which are oxidized to form carbon dioxide andwater. The oxidation catalyst is also referred to herein as a DieselOxidation Catalyst (DOC).

The NOx storage converter 18 contains a NOx storage catalyst togetherwith a DOC for HC and CO oxidation. In examples of the presentdisclosure, the NOx storage converter 18 also contains a HC storagematerial. Close coupled with the diesel engine 12, the NOx storageconverter 18 passively stores NOx emissions until the stored NOxemissions are released at a higher temperature. The downstream SCRconverter 22 (or SCRF converter 22′) then reduces the released NOx usingammonia. In the aftertreatment system 10, most of NOx is reduced tonitrogen gas.

Examples of the NOx storage converter 18 may include a dual-layercatalyst. In other examples of the present disclosure, the NOx storageconverter 18 may have a NOx storage catalyst and a DOC catalyst mixedinto one single layer catalyst washcoat. An example of the dual-layercatalyst includes a substrate, a NOx storage layer disposed on thesubstrate and a DOC layer disposed on top of the NOx storage layer. Thesubstrate may be any material suitable for a diesel emissions controlcatalyst, examples of which include ceramic substrates (e.g.,cordierite) or a metallic alloy (e.g., stainless steel containing Cr, Alor Ti), and combinations thereof.

The NOx storage layer includes a NOx storage catalyst for storing NOx.The NOx storage catalyst is to release the stored NOx when the NOxstorage catalyst is heated to an active temperature of the NOx storagecatalyst. The DOC layer may include the DOC for HC and CO oxidation. Thedual-layer catalyst may be achieved with a double catalyst washcoatingof the two layers, with the DOC layer formed on top of the NOx storagelayer.

The NOx storage layer and the DOC layer may be applied sequentially ontothe substrate by any suitable method. In an example, the NOx storagelayer and the DOC layer are sequentially applied by multiple washcoating(e.g., dual washcoating). Depending on the type of a given substrate,suitable NOx storage layer and DOC layer thicknesses are sufficient tomaintain a predetermined pressure drop in order to control engine backpressure.

In an example, the thickness of each of the NOx storage layer and theDOC layer, individually, ranges from about 5 micrometers to about 150micrometers. In a further example, the thickness of each of the NOxstorage layer and the DOC layer, individually, ranges from about 20micrometers to about 100 micrometers. It is to be understood that thethickness of the NOx storage layer may be the same as, or different fromthe thickness of the DOC layer.

FIG. 1 depicts an example of the vehicle 2 with a Nitrogen Oxides (NOx)storage converter 18 according to the present disclosure. In FIG. 1, theNOx storage converter 18 contains a NOx storage catalyst which alsopossesses the functionalities of a DOC for HC and CO oxidation. Theexhaust gas treatment system 10 is effective to reduce NOx to nitrogengas, and to oxidize HC and CO. The NOx storage converter 18 is toreceive exhaust gases 15 from the diesel engine 12. The NOx storageconverter 18 stores at least a minimum amount of the NOx emitted by thediesel engine 12 in the exhaust gases 15 at a temperature below astorage threshold temperature. In an example, the minimum amount of theNOx stored in the NOx storage converter at a particular time is 10percent of the NOx received from the diesel engine. For example, theminimum amount of the NOx stored in the NOx storage converter during acold start test may be at least 10 percent of the NOx received from thediesel engine during a cold start test.

In an example, “cold start” may refer to a period of time underconditions defined in 40 CFR § 86.137-94 (a), included by referenceherein in its entirety. As stated in 40 CFR § 86.137-94 (a), the coldstart test is divided into two periods. The first period, representingthe cold start “transient” phase, terminates at about 505 seconds of thedriving schedule referred to in 40 CFR § 86.137-94. The second period,representing the “stabilized” phase, consists of the remainder of thecold start driving schedule (including engine shutdown).

Examples of the NOx storage catalyst of the present disclosure store NOxbetween about 10 degrees Celsius (° C.) and about 160° C. In an example,the storage threshold temperature may be above 160 degrees Celsius (°C.).

The NOx storage converter 18 is to release the stored NOx at atemperature above a releasing threshold temperature. In an example thereleasing threshold temperature may be above 140° C. In an example, thestorage threshold temperature may be within 20° C. of the releasingthreshold temperature. The NOx storage converter 18 is further tooxidize HC, and to oxidize CO.

As depicted in FIG. 1, an input temperature sensor 52 is disposed at anentrance 28 to the NOx storage converter 18 to determine an inputtemperature of the exhaust gases 15. An output temperature sensor 54 maybe disposed at an output 34 of the NOx storage converter to determine anoutput temperature of the exhaust gases 15.

Examples of the vehicle 2 of the present disclosure include a controlmodule 50 to receive the input temperature from the input temperaturesensor 52 and the output temperature from the output temperature sensor54. The control module 50 includes circuits and/or logic to determine amagnitude of an exotherm in the NOx storage converter 18 based on theinput temperature and the output temperature. The control module 50 isto store an electronic fault code in a computer memory 36 in response tothe magnitude of the exotherm being below a minimum temperature. Theelectronic fault code indicates a reduction in a NOx storage capacity ofthe NOx storage converter.

In an example of the vehicle 2 depicted in FIG. 1, the vehicle 2includes a Selective Catalyst Reduction (SCR) converter 22 or an SCRFconverter 22′. The SCR converter 22 (or the SCRF converter 22′) may bedisposed downstream from the NOx storage converter 18 in the exhaust gastreatment system 10 to reduce the NOx in the exhaust gases 15.

The SCR 22 may include, for example, a flow-through ceramic or metallicmonolith substrate that may be packaged in a stainless steel shell orcanister having an inlet and an outlet in fluid communication with theexhaust gas conduit 14. The substrate may include an SCR catalystcomposition applied thereto. The SCR catalyst composition may contain amesoporous material (e.g., zeolite, SSZ-13, SAPO(silico-alumino-phosphate)) and one or more base metal components suchas iron (Fe), cobalt (Co), copper (Cu) or vanadium (V) which can operateefficiently to reduce NOx constituents in the exhaust gas 15 to nitrogenand water in the presence of a reductant 26 such as NH₃. In examples ofthe present disclosure, an SCRF converter 22′ may be substituted for theSCR converter 22. In examples with an SCRF converter 22′, both ceramicand metallic filter substrates can be used.

An NH₃ reductant, (e.g., DEF) may be supplied from a reductant supplysource (not shown) and may be injected into the exhaust gas conduit 14at a location upstream of the SCR converter 22 (or the SCRF converter22′) using a DEF injector 46, or other suitable method of delivery ofthe reductant to the exhaust gas 15. The reductant may be in the form ofa gas, a liquid, or an aqueous urea solution and may be mixed with airin the DEF injector 46 to aid in the dispersion of the injected spray.

With further reference to FIG. 1, control module 50 receives input fromvarious sources (e.g., input temperature sensor 52, and outputtemperature sensor 54). The control module 50 includes control logic formonitoring (and/or determining) the temperature of the NOx storageconverter 18.

The control module 50 includes control logic to activate a HC/fuelinjector 40 when the control module 50 determines that a thresholdhydrocarbon value has not been met. Upon activation, the HC/fuelinjector 40 introduces unburned HC into the exhaust gas stream. If thecontrol module 50 determines that the threshold hydrocarbon value hasbeen met, then the control module 50 further includes control logic fordeactivating the HC/fuel injector 40. Alternatively, the HC/fuelinjector 40 may be omitted, and the control module 50 may modifyoperating parameters of the engine 12 to control the hydrocarbon levelsin the exhaust gases 15. Specifically, the control module 50 adjusts theengine timing and rate/frequency of fueling to deliver excess, unburnedfuel into the exhaust gas conduit 14 for mixing with the exhaust gas 15.

In examples according to the present disclosure, control module 50 mayoperate on-board the vehicle 2 by a method 100 as depicted in FIG. 2aand FIG. 2b together. FIG. 2a and FIG. 2b together are a flow chart thatdepicts a method 100 for monitoring and diagnosing a NOx storageconverter 18 on-board a vehicle 2 according to the present disclosure.Flow chart connector A connects the bottom of FIG. 2a with the top ofFIG. 2b . The box at reference numeral 102 depicts “starting a dieselengine at a start time and operating the diesel engine therebygenerating exhaust gases.” At reference numeral 104 is “conducting theexhaust gases via an exhaust system through the NOx storage converter.”At reference numeral 106 is “measuring an input temperature of dieselengine exhaust gases flowing into the NOx storage converter.” Atreference numeral 110 is “measuring an output temperature of the dieselengine exhaust gases flowing out of the NOx storage converter.” Atreference numeral 112 is “determining an exothermic activity valueindicative of an exothermic activity of the NOx storage converter bycomparing the input temperature and the output temperature.” Atreference numeral 114 is “determining a diagnostic value by comparingthe exothermic activity value to a predetermined exothermic activitythreshold, the diagnostic value being indicative of an operational stateof both a NOx storage function and a hydrocarbon (HC) oxidation functionof the NOx storage converter”. At reference numeral 116 is “storing thediagnostic value in a computer memory.”

In FIG. 2A and FIG. 2B, some of the boxes are shown in dashed lines toindicate that the subject matter in the box is an optional element ofthe method 100. For example, as shown in the box with the dashed outlineat reference numeral 120, “the input temperature is below a diagnosticstart temperature at the start time.” At reference numeral 122, “thediagnostic start temperature is under 150 degrees Celsius.” Thus, themethod 100 may be applied at all times, or the method may be used onlyunder certain conditions, for example during a cold start. The method100 is to be applied after the NOx storage converter 18 has been exposedto a known quantity of hydrocarbons at a temperature below thediagnostic start temperature. If the NOx storage converter 18 isfunctioning, the NOx storage converter 18 will store the HC and generatethe exotherm upon heating up. If the NOx storage converter 18 isinactive it will not store the HC and there will be no exotherm uponheating up.

In the box with the dashed outline at reference numeral 126 is “storingat least a minimum amount of the NOx by adsorption in the NOx storageconverter at a monolith temperature below a storage thresholdtemperature; releasing the NOx when the monolith temperature is above areleasing threshold temperature; oxidizing hydrocarbon in the NOxstorage converter; and oxidizing carbon monoxide in the NOx storageconverter.”

In the box with the dashed outline at reference numeral 128, “theminimum amount of the NOx stored is 10 percent of the NOx received fromthe diesel engine. In the box with the dashed outline at referencenumeral 130 “the storage threshold temperature is above 160 degreesCelsius.” In an example of the present disclosure that includes theelement depicted at reference numeral 132, “the releasing thresholdtemperature is above 140 degrees Celsius.” At reference numeral 134, themethod of the present disclosure includes the optional element wherein“the storage threshold temperature is within 20 degrees Celsius of thereleasing threshold temperature.”

As depicted in the box with the dashed outline at reference numeral 136,“the determining the exothermic activity value indicative of exothermicactivity of the NOx storage converter includes determining a temperaturechange by subtracting the input temperature from the output temperature;the exothermic activity value is the temperature change; and a positivetemperature change is indicative of the exothermic activity of the NOxstorage converter.”

As depicted in the box with the dashed outline at reference numeral 138,“the determining the diagnostic value includes subtracting apredetermined temperature threshold from the temperature change; and apositive diagnostic value indicates the operational state of both theNOx storage function and the HC oxidation function of the NOx storageconverter.” For example, a positive diagnostic value may indicate thatthe operational state of both the NOx storage function and the HCoxidation function of the NOx storage converter is “good”. In otherwords, a “good” operational state may mean that NOx storage converter isoperating within specified limits for both the NOx storage function andthe HC oxidation function. Conversely, a negative diagnostic value mayindicate that the operational state of both the NOx storage function andthe HC oxidation function of the NOx storage converter is“malfunctioning”. A “malfunctioning” operational state may mean that NOxstorage converter is not operating within specified limits for both theNOx storage function and the HC oxidation function.

As depicted in the box with the dashed outline at reference numeral 124,the method may include the step of “injecting a predetermined amount ofthe HC into the exhaust gases to chemically react in the NOx storageconverter.”

An existing catalytic converter diagnostic method is disclosed in U.S.Pat. No. 5,630,315 by inventor Joseph R. Theis, referred to herein as“Theis”. Theis is included by reference herein in its entirety. Theisdiscloses steps in a catalytic converter diagnostic method whereinexothermic activity of the catalytic converter is monitored to determineif the catalytic converter is operating properly. However, Theis doesnot contemplate a NOx storage converter 18 as disclosed herein. Further,the steps in the method disclosed by Theis would not be capable ofdiagnosing the NOx storage functionality of the NOx storage converterbecause the method disclosed by Theis checks for a warmed-up engine andexits if the engine is not warmed up. Theis discloses at step 114 inTheis' FIG. 4A that the diagnostic method is not attempted until theengine has been run for greater than 200 seconds. Further, at step 112,Theis discloses that the coolant must have a temperature indicating thatthe engine is running at the normal operating temperature. Since Theisdoes not contemplate a catalytic converter with both DOC and lowtemperature NOx storage functions, Theis does not contemplate a NOxstorage converter 18 according to the present disclosure. Further, Theisdoes not disclose that exothermic activity of a NOx storage converter 18that has both a low temperature NOx storage layer and a DOC layer couldbe used to indicate the operative status of both the NOx storage layerand the DOC layer as disclosed in the present disclosure.

FIG. 3 is a graph of experimental results depicting a reduction in theexothermic activity due to oxidation of stored HC in sample NOx storageconverters at different stages of the useful life of the NOx storageconverters. The ordinate axis 62 is the outlet temperature in degrees C.The abscissa is the inlet temperature in degrees C. The temperaturespikes that are observable, for example on Trace A at about 180 degreesC., are from exotherms due to oxidation of stored HC. Trace A is datafrom a sample NOx storage converter that was aged for 24 hours at 650°C. in air with 10 percent moisture. Trace B is data from a sample NOxstorage converter that was aged for 48 hours at 750° C. in air with 10percent moisture. Trace C is data from a sample NOx storage converterthat was aged for 16 hours at 900° C. in air with 10 percent moisture.Trace D is data from a sample NOx storage converter that was engine agedto a point where the NOx storage converter is nearly inoperative.

FIG. 4 is a bar graph depicting experimental results for the samesamples shown in FIG. 3, except FIG. 4 depicts the NOx storageefficiency below 200° C. for the samples. The ordinate axis 66 is theNOx Storage Efficiency expressed as a percentage. When FIG. 3 and FIG. 4are observed together, it is notable that a small HC exotherm correlatesto a NOx storage converter that has become inoperative, and that the HCexotherm continues to be significant even when the NOx storageefficiency is reduced, but not yet inoperative. Thus, for the NOxstorage converter with a NOx storage layer and a DOC layer, the HCexotherm is an indicator of the operability of both the NOx storagefunction and the HC oxidation function of the NOx storage converter.

The discussion of the SCR converter has been presented above, in someexamples, in terms of urea as the reductant that is injected into theexhaust system for reaction with the SCR converter to reduce NOx tonitrogen and water. However, other reductants, such as anhydrous ammoniaand aqueous ammonia, may also be used in lieu of the DEF (aqueous ureasolution). If urea is used, the reduction reaction also produces carbondioxide.

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range of from about 5 micrometers to about 150 micrometersshould be interpreted to include not only the explicitly recited limitsof from about 5 micrometers to about 150 micrometers, but also toinclude individual values, such as 12 micrometers, 50.7 micrometers,etc., and sub-ranges, such as from about 40 micrometers to about 80micrometers, etc. Furthermore, when “about” is utilized to describe avalue, this is meant to encompass minor variations (up to +/−10 percent)from the stated value.

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

While several examples have been described in detail, it is to beunderstood that the disclosed examples may be modified. Therefore, theforegoing description is to be considered non-limiting.

1. A vehicle, comprising: a Nitrogen Oxides (NOx) storage converter toreceive exhaust gases including NOx from a diesel engine, store at leasta minimum amount of the NOx at a temperature below a storage threshold,release the NOx at a temperature above a releasing threshold, oxidizehydrocarbon (HC), and oxidize carbon monoxide; an input temperaturesensor disposed at an entrance to the NOx storage converter to determinean input temperature of the exhaust gases; an output temperature sensordisposed at an output of the NOx storage converter to determine anoutput temperature of the exhaust gases; and a control module to:receive the input temperature and the output temperature; determine amagnitude of an exotherm in the NOx storage converter; and store anelectronic fault code in a computer memory in response to the magnitudeof the exotherm being below a minimum temperature, wherein the faultcode indicates a reduction in a NOx storage capacity of the NOx storageconverter.
 2. The vehicle as defined in claim 1 wherein the NOx storageconverter is further to store the HC when a monolith temperature in theNOx storage converter is below the storage threshold.
 3. The vehicle asdefined in claim 1 wherein the at least the minimum amount of the NOxstored is 10 percent of the NOx received from the diesel engine.
 4. Thevehicle as defined in claim 1 wherein the storage threshold temperatureis above 160 degrees Celsius.
 5. The vehicle as defined in claim 1wherein the releasing threshold temperature is above 140 degreesCelsius.
 6. The vehicle as defined in claim 1 wherein the storagethreshold temperature is within 20 degrees Celsius of the releasingthreshold temperature.
 7. The vehicle as defined in claim 1, furthercomprising a Selective Catalyst Reduction (SCR) converter, or aSelective Catalyst Reduction in Filter (SCRF) converter, disposeddownstream from the NOx storage converter in an exhaust gas treatmentsystem to reduce the NOx in the exhaust gases.
 8. A method formonitoring and diagnosing a Nitrogen Oxides (NOx) storage converter on avehicle comprising: starting a diesel engine at a start time andoperating the diesel engine thereby generating exhaust gases includingNOx; conducting the exhaust gases via an exhaust system through the NOxstorage converter; measuring an input temperature of the exhaust gasesflowing into the NOx storage converter; measuring an output temperatureof the exhaust gases flowing out of the NOx storage converter;determining an exothermic activity value indicative of an exothermicactivity of the NOx storage converter by comparing the input temperatureand the output temperature; determining a diagnostic value by comparingthe exothermic activity value to a predetermined exothermic activitythreshold, the diagnostic value being indicative of an operational stateof both a NOx storage function and a hydrocarbon (HC) oxidation functionof the NOx storage converter; and storing the diagnostic value in acomputer memory.
 9. The method as defined in claim 8 wherein: thedetermining the exothermic activity value indicative of exothermicactivity of the NOx storage converter includes determining a temperaturechange by subtracting the input temperature from the output temperature;the exothermic activity value is the temperature change; and a positivetemperature change is indicative of the exothermic activity of the NOxstorage converter.
 10. The method as defined in claim 9 wherein: thedetermining the diagnostic value includes subtracting a predeterminedtemperature threshold from the temperature change; and a positivediagnostic value indicates the operational state of both the NOx storagefunction and the HC oxidation function of the NOx storage converter. 11.The method as defined in claim 8 wherein the input temperature is belowa diagnostic start temperature at the start time.
 12. The method asdefined in claim 11 wherein the diagnostic start temperature is under150 degrees Celsius.
 13. The method as defined in claim 8, furthercomprising: storing at least a minimum amount of the NOx by adsorptionin the NOx storage converter at a monolith temperature below a storagethreshold temperature; releasing the NOx when the monolith temperatureis above a releasing threshold temperature; oxidizing hydrocarbon in theNOx storage converter; and oxidizing carbon monoxide in the NOx storageconverter.
 14. The method as defined in claim 13 wherein the minimumamount of the NOx stored is 10 percent of NOx received from the dieselengine.
 15. The method as defined in claim 13 wherein the storagethreshold temperature is above 160 degrees Celsius.
 16. The method asdefined in claim 13 wherein the releasing threshold temperature is above140 degrees Celsius.
 17. The method as defined in claim 13 wherein thestorage threshold temperature is within 20 degrees Celsius of thereleasing threshold temperature.
 18. The method as defined in claim 8,further comprising injecting a predetermined amount of the HC into theexhaust gases to chemically react in the NOx storage converter.